1. Field of the Invention
One disclosed aspect of the embodiments relates to an information acquiring apparatus and an information acquiring method of acquiring information of a sample by using a terahertz wave.
2. Description of the Related Art
In recent years, various inspection technologies using electromagnetic waves with frequencies in a range from 30 GHz to 30 THz, so-called terahertz waves, have been developed. Japanese Patent No. 4046158 describes a measurement method for executing a nondestructive inspection by using transmissivity of a terahertz wave. This method irradiates a sample with an ultra-short pulse of a terahertz wave, detects a reflected wave from the sample to obtain a time waveform, and checks the configuration and state of each layer of the sample from the time waveform.
As indicated by P. U. Jepsen et al., Optics Letters, (2007), 15, 14717, a peak waveform of a time waveform may be checked in detail, and a complex refractive index spectrum at a position near an interface corresponding to a peak waveform may be obtained. It is known that many materials have specific absorption in a frequency band of terahertz waves, providing expectations for a new method of material analysis. Also, Japanese Patent Laid-Open No. 2011-112548 discloses a technology that measures a refractive index distribution of a front surface of a living body sample for a terahertz wave, and visualizes the result. Such an inspection technology using a terahertz wave provides expectations for application to medical use, such as pathologic diagnosis using a phenomenon in which the refractive index and reflectivity of a living tissue vary depending on a portion and a state (normal cell or tumor cell).
In measurement with a reflection system, a terahertz wave reflected by a mirror is measured in addition to a terahertz wave reflected by a sample, and acquires information of the sample by using time waveforms of the terahertz waves. However, if the positions of the front surface of the sample and the front surface of the mirror are not the same, or if the intensity of a terahertz wave varies every measurement, correct comparison cannot be made, and hence measurement accuracy may be decreased. To address this, a method for measurement by using a plate-shaped transmission member that transmits a terahertz wave is used. This is a method of irradiating a sample with a terahertz wave through a transmission member while the transmission member contacts the sample.
In the past, various types of measurement have been executed based on an assumption that the transmission member has a uniform thickness in plane. However, it is difficult to manufacture a transmission member with a uniform thickness in plane. The expected thickness may differ from the thickness at an actually measured position, or the thickness of the transmission member may vary every irradiation position of the terahertz wave. Hence, it is difficult to constantly satisfy accuracy which is currently expected.